Penicillium Mold

Blue cheeses use mold – Penicillium roqueforti – to get their distinctive veins. And a fun cheese history lesson that connects the Manhattan Project to cheese!

What’s Penicillium roqueforti?

Let’s start at the top of the living organism hierarchy: fungi. Alongside plants and animals, fungi are a “kingdom” of living organisms. Underneath the umbrella of fungi are yeasts and molds. Underneath mold we find today’s topic: the genus Penicillium.

plate blue cheese

Penicillium roqueforti isolated from a Wisconsin blue cheese. (i.e. the extent of microbiology prowess)

If we zoom in even further we find Penicillium roqueforti, which we’ve talked about already here and here. P. roqueforti are little enzyme factories that create the distinctive flavor, aroma, and appearance of blue cheeses the world around. If you zoom into these little guys you’d see a messy hair of filaments known as mycelia. Each of these filaments are known as hyphae (singular: hypha). You can think of these are the little sprouts/stems that mold grows from. If there happen to be an mycologists currently reading this, I sincerely apologize for my gross oversimplification.

mycelium blue cheese

Blue mold grows in structures known as hyphae.


Types of P. roqueforti

Now that we’ve gotten the introductory information out of the way, I must make a confession. I, along with most cheese technologists, usually say something along the lines of Penicillium roqueforti is used for Roquefort and Penicillium glaucum is used for Gorgonzola. This is a bit of a half-truth. Names like P. glaucum, P. stilton, etc. are known as “technological” species. Actually, they are all sub-species of P. roqueforti. This species of mold is enormously diverse and is found not only in many distinct blue cheeses, but across the food world and the natural world. And it can look quite diverse too!

penicillium types

P. roqueforti is very diverse and its appearance can be just as diverse. Check out the research paper here. (It’s open source! Yay!)

The environment in which the milk is gathered, the cheesemaking operations unique to each cheese type, and the unique aging spaces/atmospheres can all select for certain sub-species of P. roqueforti. This results in the unique flavor and appearance we’ve all grown accustom to in some of the worlds most famous cheeses.


P. roqueforti Metabolism

Penicillium roqueforti has quite an active metabolism. It breaks down protein and fat very effectively. This yields the textures, aromas, and flavors that we all know and love (or revile in some cases). For this post, we’re going to focus on fat and the breakdown of fat – lipolysis. As we’ve learned before, fat occurs in structures called triglycerides. Triglycerides are made of fatty acids. Mold metabolism can free these fatty acids and break them down even further into a menagerie of flavor compounds. One family of molecules – ketones – are very important to blue cheese aroma/flavor.

ketones in blue cheese

Mold helps with lipolysis – the breakdown of fat – which ultimately results in ketones. Heptan-2-one is the most famous for causing “blue” flavor.

Just like we need to breath to have a healthy metabolism, so does P. roqueforti. When starved of oxygen, blue mold metabolism adjusts and results in nasty colors/flavors. So remember, never vacuum pack blue cheese!

blue cheese oxygen blue cheese no oxygen

Drag the slider to see the difference between healthy blue mold and oxygen-starved blue mold! Made using twentytwenty.js


nuworld Cheese

During the late 1940s, genetics Professor H.J. Muller, who worked as an advisor on the Manhattan Project, exposed fruit flies to X-ray radiation and studied the resulting mutations. Bacteriology Professor Stanley Knight, of the University of Wisconsin, was inspired by this work and decided to expose Penicillium roqueforti to UV lights to see what mutations might occur. Interestingly enough, he created a mutant strain that didn’t turn blue – it was white. He partnered with Professor Walter Price, one of the most prolific cheese scientists in history, to see what kind of cheese this mutant would make. Due to space constraints in the lab, they partnered with the University of Minnesota to make cheese. The cheese they created was flavorful like blue cheese, but you couldn’t tell by looking at it! This cheese was so uniquely American, they gave it a fitting name: nuworld cheese.

nuworld cheese

You can buy nuworld cheese from University of Minnesota Food Science Dept.

Read more about this fascinating cheese here!